1. Field of the Invention
The present invention relates to a position detection technology, and, more particularly to a position detecting apparatus that can automatically detect, when an original sheet or the like is conveyed while sliding in a state in which both side edges in a paper width direction thereof are in contact with a guide, width of the original sheet or the like from a position of the guide and an image processing apparatus provided with the position detecting apparatus.
2. Description of the Related Art
Conventionally, in the position detecting apparatus of this type, switches or sensors that can represent two values are arranged in a reading position as means for detecting a position of a mechanical member that mechanically moves. In this case, the number of the switches or sensors arranged corresponds to resolution (digits) required for position detection. FIG. 11 is a perspective view simply showing a position detecting apparatus 500 that is used for paper width detection used in a copying machine and the like. This position detecting apparatus 500 includes a slide plate 51, a sheet guide 52 fixed at one end of the slide plate 51, bit mark reading sensors 61 to 64 (in this example, reflection sensors are used) arranged in a reading position near the other end of the slide plate 51, and a not-shown position deriving unit made of an electronic circuit.
The slide plate 51 serving as a moving mechanical member is constituted to be capable of sliding in a direction indicated by an arrow DN. In this example, binary numbers of four digits are appended to a lower surface of the slide plate 51. In this case, the binary numbers are represented by white or black marks (bit marks) in association with logics of respective bits of the binary numbers. Bit marks of the respective digits of the binary numbers are appended at equal intervals in a direction orthogonal to the slide direction. Bit marks of an identical digit of the respective binary numbers are appended at fixed pitches (referred to as steps P0 to P15) in a linear shape along the slide direction DN.
In other words, the respective bits of the binary numbers are arranged at intersections of four imaginary straight lines that extend at equal intervals in the slide direction on the surface of the slide plate and sixteen imaginary straight lines that are orthogonal to the four imaginary straight lines and extend at intervals of fixed pitches. In the positions of the respective bits, “1” is displayed as a white bit mark and “0” is displayed as a black bit mark. It goes without saying that other colors may be used as long as the binary numbers can be digitally displayed.
In the case of FIG. 11, a not-shown fixed wall is provided at the other end of the slide plate 51. An original sheet or the like to be copied is placed between the sheet guide 52 and the fixed wall. The sheet guide 52 is slid in the direction of the arrow DN. Both side edges of the original sheet are brought into contact with the sheet guide 52 and the fixed wall, respectively. In other words, the original sheet is held to be capable of slidingly moving between the sheet guide 52 and the fixed wall. In the case in which the position detecting apparatus 500 is operating, when the slide plate 51 is slid and a position of the sheet guide 52 is set to width of the original sheet, the sensors 61 to 64 read logics indicated by bit marks of the slide plate 51 facing the sensors 61 to 64. The not-shown position deriving unit derives, on the basis of the logics read by the sensors 61 to 64, positions of the steps P0 to P15 indicated by binary numbers represented by the bit marks read. A host apparatus determines, for example, width of the held original sheet or the like on the basis of a result of the derivation.
In the example described above, positions of the slide plate 51 are represented by the bit marks of the binary numbers. However, as shown in FIG. 12, the binary numbers are simple ones obtained by directly using usual binary numbers. Overall display by the bit marks appended to the surface of the slide plate 51 is referred to as a bit matrix. When logics indicated by two bit marks that belong to a same digit of the binary numbers in the bit matrix and are adjacent to each other in a front-to-back direction with respect to the slide direction of the slide plate 51 are opposite, a point between these bit marks is referred to as a bit change point.
In the case of FIG. 12, there are plural bit change points (indicated by underlines in FIG. 12) where plural bits in the binary numbers adjacent to each other with respect to the slide direction of the slide plate 51 simultaneously change. Therefore, when the moving mechanical member stops at a bit change point or near the bit change point, it is impossible to decide values of which bits are adopted before and after the change points. In this case, depending on a combination of values of bits adopted, the mechanical member (the slide plate 51) is likely to be recognized as stopping in a position distant apart from a position where the mechanical member actually stops.
As described above, in the conventional position detecting apparatus, when the moving mechanical member (e.g., the slide plate 51) stops near the bit change points, it is impossible to decide which values are adopted before and after the respective bit change points. In such a case, the mechanical member is likely to be recognized as stopping in a position distant apart from a position where the mechanical member actually stops. For example, in the case of FIG. 12, when it is assumed that a position where the mechanical member stops facing the sensors 61 to 64 is between the step P7 (0111) and the step P8 (1000) of the slide plate 51, it is likely that bits of all the digits are read as “1” or “0”. In other words, it is impossible to decide which of binary numbers (0000) to (1111) the position takes. Thus, in order to eliminate this uncertainty, conventionally, respective sensors are accurately arranged such that changes of bits are always performed simultaneously or machining accuracy is improved to prevent play (back-lash) from occurring in a moving mechanism. Alternatively, complicated measures are taken. For example, a latch mechanism or the like is used such that the mechanical member such as the slide plate 51 stops only in a regular position of binary numbers without stopping at the bit change points.
Related techniques are disclosed in JP-B-2-22570 (gray codes are used for A/D conversion) and JP-A-2002-332120 (a mechanism of a slide plate).